Call-distributing system



April 19, 1927. 1,625,624

W. T; PQWELL CALL DISTRIBUTING SYSTEM Filed Marchfil. 1920 4 ts-Sheet JCDFFiCE *2 FKE. 1

TELEPHONE SET.

ENJENTOE WIHFRED T POWELL ATTGRNEY April 19 1927.

FIG. 2

W. T. POWELL CALL DISTRIBUTING SYSTEM Filed March 31. 1920 4Sheets-Sheet. 2

B POSVHON POSITKSH RELEfiSE KEV l a f P i 1 I I I I I P I 8 l l l ,9INVENTOR &5 WINFQED T. POWELL \AJW 0 BY ATTO EY April 19 1927. 1,625,624

w. T. POWELL CALL DISTRIBUTING SYSTEM Filed March 51. 1920 "4Sheet-Sheet s BPOSITI Fig.2. A

Pos wl n B PO5\T\OH, RELEASE KEY.

TRurmka f3 INVENTOR 5 wmFRED TPOWELL nun ATTORNEY April 19,1927.1,625,624

W. T. POWELL CALL DISTRIBUTING SYSTEM Filed M arch 31. 1920 4Sheets-Sheet 4 OPER m-o Rs SET.

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INVENTQR WHiFRED T POWELL ATTORNEY Patented Apr. 19, 1927.

UNITED STATES PATENT OFFICE.

WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROM BEFRG-CARLSON TELEPHONE MANUFACTURING GOMIANY, OF ROCHESTER, NEW YQRK,

CALL-DISTRIBUTING SYSTEM.

Application filed March 31, Serial No. 370,142.

This invention relates to telephone sys tems, and more particularly to.telephone systems in which automatic switches are employed to distributecalls to. various operators.

In manual telephone systems of relatively large size it is necessary inthe case of certain calls that the connection be completed through twoor more ofiices. In accordance with the practice formerlyemployed, forsuch cases a so-called order wire extending between the two oificesserves as a means over which the operator at the first oiiice, known asthe A operator, was able to repeat the wanted number to the operatoratthe second office who, is known as the B operator. I I

Briefly the operation of extending a call in such a manual system,involves the connection of the answering endof the A operators cordcircuit to the calling line, and this operator receives the designationof the wanted line. She thereupon instructs a B operator at the wantedoffice of the number of the wanted line over an order wire, and the Boperator instructs the A operator over the same order wire of thenumber, of the trunk to be used. The A operator then inserts the callingend of the cord circuit into the jack of the trunk circuit designated.

In the present invention the order wire has been omitted and in itsstead a series of trunks and automatic switches are employed. In thepresent system on the initiation of a call the A operator inserts theanswering end of her cord circuit into the jack of the calling line andreceives the designation of the wanted line. She thereupon inserts thecalling end of her cord circuitinto any one of a plurality of jacks oftrunks leading to the wanted oifice. A trunk selecting switch thenselects an idle trunk leading to the wanted oliice where primary andsecondary switches select idle trunks to connect the calling line to a Boperators position. While these switching operations are taking place, atone is transmitted to the A operators telephone set to inform her thatthe B operator is not in readiness to receive the call. When, however,the tone is discontinued, the A operator repeats the designation of thewanted line and the B operator after testing the wanted line and findingit idle, inserts the calling end of her cord circuit into the jack ofthe wanted line. The

signaling of the wanted line and the other claims.

The drawings with Fig. 2 placed at the right of Fig. 1 diagrammaticallyrepresent a telephone system having one or more B operators" positionsand in which a predetermined number of calls are apportioned to each Boperators position, and when this predetermined number of calls areunanswered at this B position no other calls can be extended thereto. InFig. 1 there "is diagrammatically represented anoflice designated #1 andpart of a second office #2. In oflice #1 there is represented a callingsubscribers line and its associated equipment. A cord circuit at the Aoperators position is also indicated, and the circuits of the trunkselecting switch for selecting anidle trunk to a wanted office are shownat the left of the dotted line. At the right of the dotted line there isshown the equipment of 05cc #2 for selecting an idle B operatorsposition. In Fig. 2 there is shown one plug ended trunk circuitindividual to this position, as well as other equipment be low thedotted line common to all trunk circuits of this position. At the upperright hand corner of Fig. 2 there is shown a telephone line, hereinreferred to as the called line. Figs. 2 and 3 when substituted for Fig.-2, represent a modified form of the invention, in, which overflowpositions are Shown. its many of these positions will he provided as arenecessary to care for traliic which cannot he handled by the regular Boperators positions. Corresponding parts of Fin". 9 are designated bythe same reference characters as are used in Fig. 2.

The switches of the present invention may he of the structuresubstantially similar to that disclosed in the patent to Clement,#1,107,153, patented rcugust 11, 1914.

It Will he understood that the equipment of ollice :g'il, such as theoperators cord circuit as well as the operatofis telephone set, Will beof the character of those now in use in manual common battery telephonesystonne.

Several of the relays, notably 10, 525 and 33 have contacts designated Xwhich indicates that these contacts close before other contacts on theassociated relay are operated.

It is believed the invention will best be understood by descrihinp; themethod of extending a call from a calling substation, such as A to acalled substation such as B, and subsequently explaining the method ofextenliling; the calling line to a second called suhstation, such as C.

l l hen the calling: S iiscriber at A initiates a call by removing; hisreceiver from itn switchhoolt, the line relay LR individual to his line,is energized over a circuit controlled at back contacts of the cut-oilrelay CO, and this relay is actuated to li ht the lamp a sociated withthe anion c jack (3 of the calling line. The operator on noting thatlamp 5 is lighted, inserts her answering plug 7 into the jack ll. Thisoperation causes the cut-otl' relay CO to he energized, whichdeenergizes the line relay lull, which in turn extinguishes the lamp Theoperator thereupon depresses her lis-iteninp; hey LK which counccts hertelephone set in ln'idge of the n utering end of her cord circuit andascer Kaine from the calling party the deF'guation ot the wanted otliccand the desired line term inatingr thcrcat. The operator then insertsthe calling; plug: 3 oi the cord circuit which she has taltcu tor useinto onc oi a group oi jacks fl, thr uc'h which the wanted oliicc may hereached. oon an the plug 5'? is; inserted into the jaclt the relay lollis operated in a circu t clcwezgl troui oroundwinding Oil the relay l l.elecrc at the jzu-l' ll, sleeve of the plug ti, winning ol re; ll whichcontrol;

a supervirory relay (not shown) to grounded battery. The re ay ll)attracts llt-E armatures, and a; its middle armature connects a toneovcr conductor 12, inneuniost upper back contact and armature of relaythrough the lower side oi the cord circuit, the operators telephone set.upper ride of the cord circuit to ground, through the supervisory relay14-. This tone or a similar tone Will he applied to the A oncratorsheadset until the P) operator is ready to receive the designation of thewanted line.

At the iuner-nurt armature ol relay in, a circuit in closed l'romgrounded battery, rceistance, winding, nrn'ialure and haclc contact oi:the motor magnet 15 of the distributor switch, lower back contactandarmat urc of relay 3, inneranost trout contact and armature of relay toground. Under the control of this circuit, the dietrilnitor au'itchadvances its brushes progressively until its; tcet brush l6 encountersthe test terminal oi an idle trunk leading to the wanted ollice. Thisidle condition indicated by the pros-:- euce of: ground potential on itstest terminal.

liJGt it he assumed that the first idle trunk circuit tested lift thedistributor switch is the one Whose conductors are designated. 17 andltl in Fin. 1. As noon 8?} thiu t'lllllli' is tested, a circuitcompleted troin ground, outer armature and hacl: contact of relay 19,teat terminal o'l this trunk, test ln'ush 16, upper winding ot relay lwhich has low resistance outer-moat trout contact and arn'iature ofrelay 1t), resistance, to grounded battery. This circuit shunts theSlifllflDlllg n'iagnetof the dietrilinitor ewitch to stop the Fame andalso energizes the switching relay This last named relay attracts itsarniatures, and at its lower armature and :lront contact closes aholding circuit for itself through its high resistance Winding, fromground, innermost armature and trout contact 0t? relay ltl, armature,tront contact and Winding o't relay 13, holding hrush 20, over theholding terminal of the eelected trunk and Winding of relay 19 togrounded battery. At the upper arnnilurcs ot the switching: relay 13,the callinp; line l'a extended to the wanted otlice. At the outerarmature and back contact of relay it), a guarding condition is placedon the teat terminal ot the selected trunk. it the inner front contactand arn'iature of relay 19, a hreal; point: in the conductm ill isclosed. This conductor ll extends a circuit for relay but this relayshort circuited by ground at the armature-i and back contacts of relayssimilar to l9 associated with idle truulc ot the ,ca-onp. l l ou'ever,as soon a: all the trunks these various eluiutiup; circuits are removedand the relay 53:2 attraij tn its arniiat-ures to control the operation. ot': the meter 2?) and ot a visual aigual 24- at the poieition tonotify the A. operator that all the outgoing trunks,- of a particulargroup are in use. As soon as the conductors l7 and l8 ot the selectedtrunk are extended to the Wanted otlicc, relay in operated in a circuittraceable lrom grounded battery, left hand Winding of this relay,upper-most hack contact and arunituro of relay 26 to ground, through thewinding of the relay 1 lot the A operators cord circuit. At the lefthand armature and trout contact ol relay a tone is extended over of thgroup arc ong agei'l.

fill

llO

conductor 27. This second tone is applied to the A o] )erators headsetas soon as the first tone is removed so she will know that the Boperator is not ready to receive the wanted number. At the outer-mostarmature and front contact of relay a circuit is closed from ground,back contact. armature and winding of the motor magnet 28 of adistributor switch which will be designated a primary switch,resistance, to grounded battery. Under the control of the motor magnet28, this primary switch advances its brushes until its test brush 29'encounters the test terminal of an idle trunk.

Let it be assumed that the trunk whose conductors are designated 30 and31 is the first idle trunk tested. A circuit will thereupon be closedfrom grounded battery, re sistance, inner armature, front Contact andwinding of relay 25, upper winding of relay 26, test brush 29, conductor32, outer left hand armature and frontcontact of relay 33 to ground atthe armatures and back contacts of a group-busy relay 34 to stop theprimary switch and operate relay 26. As soon as the relay 26 attractsits armatures, it closes a holding circuit for itself from ground, itslower winding, lower armature and front contact, holding brush 35,winding of relay 33 to grounded battery. As soon as the relay 33 isoperated, it extends a tone to the A operators headset over conductor 36and its inner left hand contact and armature, and at its outer left handarmature applies a busy condition to the selected trunk. At the outerright hand armature and front contact of relay 33, a circuit is closedfrom ground, lower-most armature and back contact of relay 37, armature,back contact and winding of the motor magnet 38, resistance, to groundedbattery. Under the control of this motor magnet, the secondarydistributor switch herein called the secondary switch advances itsbrushes to find an idle trunk circuit leading to a final connectingoperator. The idle condition of the trunk will be indicated bythe'presence of ground on its test terminal applied over conductor 58and controlled at the outer right hand front contact and armatureofrelay 69, so that when the test brush 41 encounters an idle testterminal a circuit will be closed through the lower winding of relay 37.innermost right hand front contact and armature of relay 33, resistance,to grounded battery. This circuit energizes the relay 37 and shunts themotormagnet 38 to stop the secondary switch. Relay 37 when energized,closes a locking circuit from grounded battery, its upper winding,lower-most front contact and armature, outer-most right hand frontcontact and armature of relay 33 to ground. At its upper armatures andfront contact the A operators telephone setcis connected to a trunkcircuit terminating in armature and back contact of relay ary switches.

a plug at a B operators position. At the upper back contact and armatureof relay 37, the tone is no longer communicated to the A operatorsheadset, thus informing her that the B operator is now ready to receivethe wanted number. As soon as the last mentioned trunk is seized, itsrelay 42 is energized over a holding brush 43, innermost, lower'frontcontact and armature of relay 37, holding brush 35, lower front contact,armature and winding of relay 26 to ground. A relay similar to 42 isprovided for each trunk ofthe group to which the secondary distributorswitch has access. As soon as the A operators cord circuit has beenextended over the trunk conductors 43 and 44, the relay 45 of Fig. 2 isenergized over the two sides of the link circuit and operators cordcircuit in series, through the winding of relay 14 to ground and togrounded battery (not shown). The relay 45 attracts its armature andcloses an op erating circuit for the slow releasing relay 46, whichattracts its arinatures to close cir cuits hereafter described. At theleft hand armature and front contact of relay 46, a circuit is closedfor actuating the slow releasing relay 47.

Simultaneously with the operation of the relay 45, the relay 48 isoperated in a circuit closed from grounded battery, winding of thisrelay, inner lefthand back contact and armature of slow releasing relay49, conductor 50, over the remainder of the circuit in multiple with therelay 42, to ground through the lower winding of relay 26 of Fig. 1. Therelay 48 is operated in this circuit and at its left hand'armature andfront contact closes a circuit which will flash the lamp 51 in acircuit-including the interrupt-er 57. The flashing of the lampindicates to the B operator that a call is coming to her position andthat she should be in readiness, to care for the same. At the innerright hand front contact and armature of relay 48, a circuit is closedfrom grounded battery, over conductor 58, conductor 67, left handwinding of the relay 59 to ground which operates to place a guardingpotential temporarily on all idle trunks of the position, so that noother calls can come to this operators position until she has completedthe call which waiting attention. This is accomplished by the openlng ofthe test circuit at the inner left hand The relay 59 at its outer lefthand contact closes a circuit including conductor 68, lower winding ofrelay 34 of Fig. 1 to grounded bat tery. Relay 34 attracts its armaturesand removes ground potential from the test terminals of idle trunks fromthe primary switch terminating at this group of second All of the trunksout from the secondary switch will be blocked at this time (though notbusy) because they all go to this position which is temporarily engaged.

In the event that all the trunks terminating at the secmulary switch arebusy, all the relays 4-2, one of which is individual to each trunkleading from the secondary switch are operated to remove a short circuit[real the upper winding of relay El -l: and to close av holding circuittroin grounded battery, resistance. iront contacts and arinatures ofrelay a, and upper winding of relay il -l to ground. it will beunderstood tha; when any trunk of this group extending from thesecondary switch hccoines idle, that its associated relay 42 will he(lo-energized and again short circuits the upper winding ot relay Illsothat the primary switch can -function again. The group relay B l: oiFig. 1 will also be operated whenever there is no operator at theposition under consideration. At this time the relay ll!) which is inseries with the opemtors trainuuitter circuit is tie-energized becausethe operator on leaving the position will disconnect her telephone set.Relay 69 on (lo-energizing will extend ground over conductor (38 tooperate the relay 31 in the manner previously described.

As soon as the relay 4-6 attracted its armatures a circuit "as closedfrom ground, inner armature and back contact ot relay 55, outer righthand front contact and armature of relay -"l-6, winding of slowreleasing relay 54, right hand armature of relay 49 and its backcontact, and winding of relay to grounded battery. Belay 52 attracts itsarinatures and connects the B operators telephone set to the trunkcircuit over which the call is being extended. The 13 operator thereuponreceives the designation of the wanted line and inn'nediately makes herposition available to other calls by depressing the position release key60, or she can proceed to insert her calling plug into the multiple jackof the wanted line attcr which this operators position will beautomatically made a *ailable to other calls.

'lwo meters (323 and (l?) are provided, the 11st to indicate the numberof times that uicralur s position is unblocked by de-- pres-dug the hey(ll) which is th method that the operator instructed to l'ulluw s nce itinsures more rapid. haiulling of calls. and the serord meter (3?: showsthe total number of calls completed at this position. l y comparing thermu'lings on the two meters a supervisor can determine whether theoperator is following instructions.

it will he assumed that the operator depresses her position release heytill to render -ailablc her position to succeeding calls. As soon as keyis depres ed. a circuit is closed from ground. left hand winding of,relay (ll, right hand winding o l relay ill. in

mars al series, outer right hand armature and front contact oi? relay4E8, continuity spring 62 and winding o't relay 4-9 to grounded battery.These relays are energized in this circuit and the relay 61 completes alocking circuit for itself and closes an operating cir cuit for themeter magnet (33 through its outer left hand front ccmtact and armature,its lett hand winding, ari'natrne and trout contact tocground. Relay 4-9on ei'ie'rgizalion closes a locking circuit for itself through itscontinuity spring (32, its right hand armature and winding of relay 54c,outer right hand armature and trout contact of relay 46, inner backcontact. and armature ot' relay an to ground. At the inner left handarnuuure and bacl; c n1tact of relay if). the actuating circuit of relay48 is opened. causing this relay to de-energize, and thereby disconnectthe lamp 51 from the interrupter and extinguishing the same until thelamp 5i is again lighted at the time o l? diwounectiou as will befurther described. lit the outer left hand armature and bacl; contact atrelay 419 a break point is opened in the conductor 58 which wouldotherwise complete a test circuit at the right hand armature and backcontact of relay 48. The opening of this test circuit renders the trunl:in use unselectable.

Z'The deenergization of relay 4.8 also opens at its inner right handarmature and front contact the operating circuit of the relay 59 whichhas previously been energized to hold the ope 'ators' p r-;i.tionunselectable.

As soon as the operator received the designation oi the wanted line andwhile the several operations just described have been taking place, shetouches the tip of her plug to the sleeve of the wanted line toascertain whether or not this line is idle. It busy, this lastinentionedoperation will cause a distinctive click in her headset since the busycondition of the called line will be indicated by battery potential onthe sleeve o'li its jack, and this potential will be extended throughthe righthand armature and hacl: contact of relay to ground, overconductor 56 which has included therein a coil intlucl'ircly connected,to the operato1"s receiver.

Let it he assumed that the wanted line. is idle in which orcnt theoperator will insert her plug l into the jack .l of the wanted line. Inresponse to this operation, the sleeve relay 5:) will be operated inseries .wilh the cut-oli' relay oi the wanted line. These relays a rethus energized and attract their armatures. At the right hand armatureof relay to. the test conductor 56 is opened and at the inner left handarmature and trout contact oi? relay 55, a circuit is closed 'lroniground, winding of the relay (i l, conductor 70. and winding of therelay {l to grounded battery. The relay 64 is ltll) contact andari'nature of slow releasing relay 54, winding of the meter magnet 65 togrounded battery. This meter as has been described, registers the numberof completed calls. Vith relay 64 operated, a circuit is cloied from theringing generator, middle armature and contact of relay 47,

armature and back contact of relay 71, winding of the trip relay TRIP,front contact and upper arn'iature of relay 64, tip of the plug throughsubstation circuits and. bell of the wanted station, ring contact of thejack and plug, inner armature and front contact of relay 64, andresistance to grounded battery. The called party is thus signaled overthis circuit and the calling party receives ringing induction throughthe resistance 72 to inform him thatthe called'party is being signaled.When the called party responds the marginal trip relay operates, and atits armature and front contact short circuits the relay 64 whichdeenergizes to close a break pbint in the ring conductor of the trunkinuse and also to short circuit resistance 72.

The calling subscriber receives talking battery through the windings ofrelays 160 and 161 while the called party receives talking batterythrough the windings of relay 71. Relay 71 is energized in this circuitand places a short circuit about the high resistance winding of relay 45which may have a resistance of 12000 ohms.

\When the calling party terminates the call, the answering supervisorysignals are lighted in the well known manner, and when the called partyreplaces his receiver on its switch hook, relay 71 de-energizes andremoves the short circuit which exists about the left hand or highresistance winding of relay 45. With this high resistance included incircuit'including conductors 43 and 44, the calling supervisory signalis lighted. After receiving these disconnect signals by the lighting ofthese supervisory lamps the A operator withdraws the plug 7 from thejack of the calling line and the plug 8 of her cord circuit from thejack of the selected trunk. As soon as this takes place, the relav 45tie-energizes and interrupts the oper ating circuit of the slowreleasing relay 46. This last mentioned relay releases and thesupervisory lamp 51 of the B operators position is caused to glowsteadily in a circuit extending from grounded battery, lamp 51, lefthand armature and back contact of relay 48, outer left hand armature andfront contact of relay 55, inner armature and back contact of relay 46to ground through resistance 81 which may be a pilot'relay common to the.POSJIOD. The operator on notlng that lamp 51 is burning steadily knowsthat the conversation has been completed and removes the plug P from thejack J of the called line. The apparatus at the B operators position isthereupon restored to its normal position and becomes available inhandling a succeeding call.

When the A operator removes her calling plug 8 from the jack 9 of aselected trunk, the relay 10, the circuit of which was controlledthrough the sleeve of the jack 9 and plug 8 tie-energizes and at itsinner armature and front contact opens the locking circuit of theswitching relay '13. The relay 13 die-energizes to release the trunkfinder switch at oiiice #1 and effects the de-energization of relay 19which has maintained.

a guarding potential on the trunk whose conductors are designated 17 and18. The brushes of the trunk finder switch at office #1 remain inengagementwith the terminals of the trunk last used, but the brushes ofthe switch are severed from the conductors of the trunk that terminatestherein at the armature and front contacts of the relay 13. Theconductors of this trunk are also opened at another point by the removalof the plug 8 from jack 9. The release of the trunk finder switch opensthe line conductors extending between ofiice #1 and oliice #2 with theresult that the relay 45 of Fi 2 deenergizes and retracts its armature.Shortly afterward the slow releasing relay 46 deenergizes, but beforethe slow releasing relay '47 has had time to retract its armatures, a

circuit is closed from ground, armature and back contact of relay 46,inner armature and front contact of relay 47, conductor 50, brush 43,armature and front contact of relay 37, winding of relay 33 to groundedbattery, which shunts the relay 26, causing it to retract itsarmawtures. At the upper armatures of relay 26 the brushes of theprimary switch are disconnected from the conductors of the trunk thatterminate therein, and at the lower armature of this relay'its lockingcircuit is opened. This primary switch after releasing alsoremains withits brushes in engagement with the terminals of the trunk last used. Ashort time after the relay 46 retracts its armatures, the slow releasingrelay 47 de-energizes and opens the circuit which shunted the relay 26and held energized the relay 33, permitting this relay 33 to retract itsarmatures. At the outer right hand armature and front contact of relay33, the locking circuit of the switching re lay 37is opened and thisrelay retracts its armatures to release the secondary switch whosebrushes likewise. remain in engagement with the terminals of the trunklast used.

Referring to the modification shown in Figs. 2 and 3 when the overflowpositions one of which is shown in Fig. 3 are employed, each secondaryline switch will be provided with one or more sets of overflow terminalsindicated at 125, 12?, 127 and 162 of l? 1 and the regular trunks fromthese switches, instead ot extending only to one operators position, aredistributed among a group oil 1% operators positions. Furthermore, thegroup relay 3% of Fig. 1, is made common to a plurality of 13 operatorspositions, instead of being individual to one B position. l l hen thisovert-low arrangement is used in case all of the B operators pesitions,such as shown in Fig. 2 become simultaneously busy, this condition willbe in di *ated by a guarding potential on the test terminals such as -10of all trunks leading to these positions. Under such conditions it acall is extended to olliee #2, it will be further extended to overflowpositions irrespectire ot' the number 01 *alls awaiting completion atthese positions. The method of extending a call when the overflowposition arrangement is used, is substantially similar to thatpreviously described.

Let it be assumed that a subscriber at A desires to converse with thesubsc 'iber at C. The A subscriber will initiate the call by removinghis receiver from its switch hook, and this will effect the lighting ofthe lamp 5 at the A operators position. The A operator then inserts theplug 7 into the jack (3 and thereafter presses the listening key LE toconnect her telephone set to the calling line and to receive thedesignation of the wanted line. The operator then inserts her plug 8into the jack 9 01" a trunk leading to an idle trunk selecting switch atollice #1 and this switch selects an idle trunk leading to a primaryswitch at o'llice it which it is assumed is the wanted ollice. Theprimary switch now selects an idle trunk leading to a secondary switch,and since it has been assumed that all of the li operators are busy,this secondary switch will not seize any of the trunks leading to thesepositions, owing to the busy condition on their test terminals, such as10 of Fig. 1, but will seize an idle overflow trunk like that shown in Fg. 3 leading to an overflow position.

As soon as the test brush all of the secondary switch reachcs the testterminal 121' of this idle overflow trunk, a circuit is completed torthe switching relay 3? extending from grounded battery, resistance,inner right hand arn'iature and contact of relay 33. lower winding otswitching relay 3?, test brush ll, test terminal 1'37, test conductor128, armature and back contact of relay 11 0, conductor 130. armatureand trout contact of relay 19.9 which energized it this operator is ather position. conductor 131. arms ture and trout contact o l relay 1352to ground. It will he noted that his relay 132 is not operated until allthe regular ll operators positions are engaged at which time the relays59 at these positions will be actualcd to remove a short circuit whichhas previously existed about relay 1132.

soon as the secondary switch has seized overflow trunk, the conductors133 and 13-1: of this trunk will he serially included inv a circuitcompleted through the winding ot' the supervisory relay 11 at the Aoperators position and including both windings oi the relay 101 of l ig.3. The relay 101 is operate-d in this circuit and at its armature andcontact closes an operating circuit for the slow releasing relay 102,and the energiza tion of this relay ell'ects the actuation of the slowrcleasing relays 102-3 and 10-1: for purposes to be described. As soonas the switching relay 37 attract its armatures, a holding circuit forthis relay is closed from grounded battery, upper winding oi. relay 3i,its lower-most :lront contact and armature, ()lltEFlllOS'l; :l routcontact and armature o1 relay 3:3 to ground. Also the holding circult ofthe relay 215 is now extended through its high resistance winding, itslower armature and front contact, holding brush 35, inner lower arniaturc and front contact of relay 23?, holding brush =53, holdingconduc tor 13.5, lower winding of relay 100 to grounded battery. Therelay 100 is energized in this circuit, and at its upper armature opensthe test conductor 128 01 the overllow trunk in use and at its lowerarmature closes a circuit to light the signal lamp 111, to inform theoperator that a call is await- Eng attention. The circuit for the lamp111 is traceable from grounded battery, through the lamp, armature andliront contact of relay 100, conductor 136, armature and back contact 0trelay 105, conductor 137, contact 112 of the operatofls listening key,contact. 113 and the interrupter to ground. Under the control of thisinterrupter the lamp 111 is flashed to inform the operator that a callis "aiting at her position. The operator at the overflow position throwsher listening key Lli to inductively coiniect her telephone set shown atthe lower right hand corner of Fig. 2}, to the trunk conductors 132:3and 134. leading to the A operators position. As in the case where theoverflow position is not used, as soon as the secondary switch hasseized an idle trunk leading to the overflow position the various tonesdisappear from the line and the i l. operator knows that it is time togive the designation of the wanted line. This designation is received bythe overflow position operator.

The operator then tests the line leading to the substation at C bytouching the tip oi the plug P to the sleeve ol the ack J. Thisoperation connects the sleeve of the jack ,1 to the operators headsetover conductor 118. It at the time the plug P is connected to the sleeveof the jack, a guarding potential was present on the sleeve, adistinctive cliel:

will be heard in the operators headset which informs her that the wantedline is engaged. Let it be assumed that the wanted line is idle, theoverflow operator thereupon inserts the plug P into the'jack J of theWanted line. This operation completes an energizing circuit for therelay 105, closed from grounded battery, upper winding of the relay 100,relay 105, sleeve of the plug P, sleeve of the jack J, through thecutoff relay herein represented as resistance 115 to ground. Relay 105attracts its armatures and at its left hand armature opens the flashingcircuit forthe lamp 111 to prevent this lamp from being flashed again onthe same call, but at its left hand'armature and front contact closes asupervisory circuit in which .this lamp will be steadily lighted at theclose of conversation as will be described. At the right hand armatureand front contact 'of relay 105, a break point is closed in theconductor 139 of the trunk that termi nates in the plug P. At the outerright hand armature and front contact of relay 105, a circuit is closedfrom ground, conductor 141, winding of relay 106, resistance to groundedbattery. Relay 106 is energized in this circuit and attracts itsarmatures to close a ringing circuit which extends from the ringinggenerator, conductor 118, inner front contact and armature of relay 103,armature and back contact of relay 109, winding of trip relay 108, upperfront contact and armature of relay 106, tip of plug P, through thesubstation circuits and bell of the substation C, ring of the jack J,ring of the plug P, inner upper armature and front contact of relay.106, resistance to grounded battery. The resistance 120 causes a toneto be transmitted to the subscriber at A to indicate that his party isbeing signaled. 'As soon as relays 105 and 106 are actuated an operatingcircuit is closed from grounded battery, winding of meter magnet 107,inner front contact and armature of relay 104C, armatures and frontcontacts of relays 106 and 105 to ground. This meter indicates thenumber of calls completed at this overflow position. When the calledsubscriber at Canswers, the trip relay 108 attracts its armature whichplaces a short circuit from grounded battery, resistance, armature andcontact of relay 108, outer right hand contact and armature of relay 105to ground about the relay 106. Relay 106 thereupon deenergizes andretracts its armatures. As soon as this takes place a circuit iscompleted for the relay 109 serially including both of its windings andthe conductors 139 and 140. With relay 109 operated the ringing circuitpreviously described is interrupted to prevent the reapplication ofringing current to the wanted line during the call just completed. Atthe left hand armature and front contact of relay 109, the highresistance left hand winding of the relay 101 is eliminated from thecircuit including the conductors 133 and 134 to control the supervisorymeans associated withthe A operators cord circuit. When the callingsubscriber at A and the called subscriber at C terminate the connection,the answering and calling supervisory lamps (not shown) of the Aoperators cord circuit are lighted in a manner previously described toindicate to her that the call has terminated. She thereupon removes theplugs 7 and 8 of her cord circuit from the jacks with which they were inengagement. This causes relay 10 to de-energize and interrupt theholding circuit of the switching relay 13. This relay deenergizes andinterrupts the holding circuit of the relay 19, which removes theguarding condition from the test terminal of the trunk that has justbeenoin use. With the conductors 133 and 134 opened, relay 101 retractsits armature and after a short interval the relay 102 retracts itsarmatures. This effects the steady lighting of lamp 111 at the overflowoperators position in a circuit completed from grounded battery, lamp111, armature and front contact of relay 100, conductor 136, left handarmature and front contact of relay 105, inner armature and back contactof relay 102, the winding of pilot relay to ground. The lighting ofthislampinforms the operator that the connection has been terminated and sheremoves the plug P from the jack J with which it has been in engagement.

The trunk just used of the overflow position is not in condition toreceive another call until the relay 100 deenergizes. This occurs whenthe B operator at the overflow position removes the plug P from jack Jafter the A operator has released her cord circuit. It will beunderstood that the energizing circuit of the upper winding of relay 100is broken at the plug P.

At the time that the A operator releases her cord circuit, relay 102de-energizes while the slowreleasing relay 10 3 is for a short time heldoperated. This places a ground potential on conductor 135 through theouter front contact and armature of relay 103, and the left handarmature of relay 102 to short circuit and release relay 26. Relay 26controls the release of the primary and secondary switches. With theseswitches released the energizing circuit for the lower winding of relay100 is interrupted. The apparatus and circuits are now in condition toreceive a second call.

In Figs. 2, 2-"- and 3 there are provided release relays 16 i and 166and release keys 165 and 167. It will only be necessary to explain thefunction and operation of the release relay 16 1 and release key 165,since the function of relay 166 and key 167 are identical therewith.These relays and release keys are provided to care for the conditionthat arises when the Jr operator momentarily inserts the plug 8 into thejack 9, and then removes this plug trom its jack. Under this conditionthe line switch at oilice :ijrl seizes a primary line switch and this inturn seizes a secondary line switch at the second oi'lice. The primaryand secon1lary switches at oll'ice #2 will remain opcrated, and thesupervisory lamp at will continue to flash. it some means like therelease relay ltil and key use were not provided, it would be impossibleto release the primary and secondary switches operated in this way. Whenan occasion arises sin'iilar to that just described, the l) operator onconnecting her telephone set to the trunk (lc;-;- ignatcd by the lamp5i. and on discoveringthat the call has been abandoned inserts the plugP into the jack associated with the re lease relay ltll. This energizesrelay int and causes it to attract its armature. The operator thendepresses key 165 and connects ground to the release trunk 50, and thisctfects the release 01 the primary switcl as as in the case oi a normalcall.

\Vhat I claim is:

1. In an automatic telephone 5 ear, a pin 'ality of incoming lines,primary trunk selecting switches for said lines, each switch beingprovided with movable brushes including a test brush and a holdingbrush, contacts for each switch arranged to be on gaged by its brushes,primary trunks terminating in the contacts of said prin'iary switches,each trunk having a test conductor and a holding conductor, means forchaactcrizing the test conductors of select able trunks by the presenceof potential and for characterizing unsclectable trunks by the absenceof potential, means for operating the brushes oi the primary line switchof an incoming circuit to move its brushes over the contacts of saidprimary trunks, means responsive to the engagementof the test conductorot a selectable trunk for stop ping said primary trunk selecting switch,a holding circuit thereupon completed including the holding conductor ofthe selected trunk for holding said primary line switch in its operatedcondition, a secondary switch in which each primary trunlr terminates,secondary trunks terminating in said secondary switches, means forcharacterizing sclcctablc secondary trunks by the presence of potentialand for characterizing unselectable trunks by the absence of potential.and means responsive to the seizure oil a primary trunk by the prin'iaryline switch :lor causing the secondary switch to seize a secondary trunkdistinguished by the presence of potential.

9. In an automatic telephone system. a

eeaeaa plurality of incoming lines, primary trunk selecting switches forsaid lines, each switch being provided with movable brushes includiug atest brush and a holding brush, contacts for each primary switch, to beengaged by the various brushes, primary trunks terminating in thecontacts or said primary switches, cach trunk having a test conductorand a holding conductor, means for characterizing the test conductors ofselectable trunks by the presence of potential and for characterizingthe test conductors of unselcctable trunks by the absence of potential,means for o 'ieratin the brushes ol the primary line switch or anincoming circuit to more its brushes over said prin'iary trunks, meansresponsive to the engagement of the test conductor oi a selectable trunkby its test brush for stopping said primary switch, a holding circuitthereupon completed through the holding brush of said primary switchincluding the holding conductor of the selected trunl; for holding saidprimary line switch in operated condition, a secondary line switch inwhich each primary trunlr terminates, secondary trunks terminating insaid secondary line switches and means re spousive to the seizure of aprin'iary trunk by a primary switch for causing the secondary lineswitch to seize an idle secondary trunk. v

ll. in an automatic telephone system, a plurality of incoming lines, aplurality of prnnary trunks terminating in said primary trunk selectingswitches, means for characterizing unseleeti ble prin'iary trunks by theabsence oi potential and for characterizing selectable trunks by thepresence of potential, means for operating a primary trunk selectingswitch of an incoming line to select a primary trunk characterized bythe presence of potential, a secondary trunk select-- .iug switch foreach primary trunk, secondtrunks terminating in said secondary switches,means for operating the secondary switch oi the selected trunlc to seizean idle secondary trunk and means for preventing the selection of aprii'nary trunlr when all the secondary trunks are in an miseiectablecondition.

1:. In an automatic telephone system, a plurality of incoming lines,primary trunk selecting switches for said lines, a group of primarytrunks terminating in said primary trunk selecting switches, means forcharacterizing unselectable primary trunks by the absence of potentialand for charactcrizimr selec able trunks by the presence of potenon.said means inclmling a relay common to said group of primary trunks,said relay being provided with sets of contacts less in number than thenumber ol primary trunks in said group. means for operating the primarytrunk selecting switch of an incomterized by the absence ot potentia lpasecond:

ary switch foreach primary trunk, a group of secondary trunks tcrm' tinginrsaidsecondary switches, means .101 operating; the seconc cry switchof the selected trunlc to" y-ti'unlt and means etseize. an idlese'conth. tfective when all the group of secondary trunks are m anuuselectable conditlon .t'or

causing said relay to characterize all of said primary trunksunsclectable.

5. in an automatic telephone system, incoming lines, primary trunkselecting switches for said lines, a group of primary trunks terminatingin said primary trunk selecting switches, means for characterizingunsclectable primary trunks by the absence of potential and forcharacterizing selectable trunks by the presence of potential, saidmeans including a relay common to said group of primary trunks, meansfor operating the primary switch of an incoming line to select a primarytrunk characterized by the presence of potential, at secondary trunkselecting switch for each primary trunk, secondary trunks terminatin insaid secondary switches, means for operating the secondary switch of theselected primary trunk to seize an idle secondary trunk, a relay foreach secondary trunk arranged to be operated when its associated trunkis seized, and means for disabling said common relay when the relay ofany of the secondary trunks is in an inert condition. I

(3. in an automatic telephone system, incoming lines, primary trunkselecting switches for said lines, a group of primary trunks terminatingin said primary trunk selecting switches, means including a testconductor for each primary trunk for characterizing unselectable primarytrunks by the absence of potential and tor characterizing selectabletrunks by the presence of potential, a relay common to said group ofprimary trunks, said relay when operated removing potential from thetest conductors of the group of primary trunks, means for operating theprimary switch or an incoming line to select a primary trunkcharacterized by the presence of potential, a secondary trunk selectingswitch for each primary trunk, secondary trunks terminating insaid'secondary switches, means for operating the secondary switch or"the selected primary trunk to seize an idle secondary trunk, a relay toreach secondary trunk arranged to be operated when its associated trunkis seized, and means for disabling the common relay when any of therelays ofthe secondary trunks are in an inert condition.

7. In an automatic telephone system, incoming lines, primary trunkselecting switches for said lines, a group of primary trunks terminatingin said primary trunk selecting swi-tches ameansctor characterizingunseleetable-=prnnary tiainles :by; the absenceof potential andforcharaeterizingselectable trunksbyith -:pre'sence of potential, ,saidmeans including; a relay common --toi :said group of primary trnnks,:-means for oper ating aida'relay; to remove potentialL-from! tie primarygroup of trunks, means for operating the primary switch of an incomingline to select a primary trunk characterized by the presence ofpotential, a secondary switch for each primary trunk, secondary trunksterminating in said secondary switches, means for operating thesecondary switch of a selected primary trunk to seize an idle secondarytrunk, a relay for each secondary trunk arranged to be operated when itsassociated trunk is seized, and means for disabling the operating meansof the common relay when any of the secondary trunks are in an inertcondition.

8. In an automatic telephone system, a phirality of incoming, lines,primary trunk selecting switches for said incoming lines, means forcharacterizing selectable trunks by the presence of potential and forcharacterizing unselectable primary trunks by the absence of potential,means for operating the primary switch of an incoming line to select aprimary trunk characterized by the presence of potential, a secondarytrunk selecting switch for each of said trunks, a second set of trunksaccessible to said seoondar 1 trunk selecting switches, said secondaryset of trunks including one or more over-flow trunks, and meanspreventing the seizure of the over-flow trunks when the remainingsecondary trunks are idle.

9. In an automatic telephone system, a plurality of incoming lines,primary switches for said incoming lines, each switch having sets ofcontacts and brushes including a test brush for engaging said contacts,primary trunks terminating in said contacts, each primary trunk having atest conductor terminating in one of said contacts, operating means foradvancing said brushes over said sets of contacts to seize a selectableprimary trunk,- a relay common to said primary trunks for normallyapplying potential to the test conductors of said primary trunks torender them selectable, means for removing said potential from the testconductor of a selected primary trunk, a secondary switch for eachprimary trunk, secondary trunks terminating in said secondary switches,means for operating said secondary switches to seize a selectablesecondary trunk, a relay for each secondary trunk arranged to beoperated on the selection of its associated trunk, and. means effectiveon the operation of all of the relays of the secondary trunks foroperating said common relay.

10. In a telephone system, incoming lines,

a plurality 01 operators positions, means including automatic switchesfor extending said incoming lines to said operators positions, aplurality of recording; devices at each operators position, means forrendering an operators position unseleetal'ile, two releasing means forrendering said operators posi tion selectable, and means including saidrecording deviees for determining which releasing means has beenemployed. 10 In witness whereof, I hereunto subscribe my name this 29thday of March, A. D.

WINFRED '1. POWELL.

